Conventionally, cylinders have been filled with compressed air by way of appropriate valves and couplings and a flexible hose connection from a pressurised source, for example as disclosed in GB No. 2200198 to the BOC Group plc. That was satisfactory, even if the connection apparatus was sometimes untidy and cumbersome, for air pressures up to and in the region of 2000 psi (141 Kg/sq cm approx), which was the standard pressure used in air cylinders for fire fighting purposes, and other portable air supply purposes. Recently, however, a requirement has arisen for air cylinders to be filled to greater pressure, in the region of 4000 psi (282 Kg/sq cm approx) so that the cylinders are less rapidly exhausted. At these higher pressures there is a risk that the flexible hose sections of conventional charging apparatus may burst open, particularly if they have any faults. This would clearly be dangerous for operatives, as well as putting the apparatus out of commission until repaired.